Volume 6, Issue 8 (September 2009)
Laboratory Tests of Water Penetration through Wall-Window Interfaces Based on U.S. Residential Window Installation Practice
Inadequate detailing practice and defective installation of windows has accounted for a significant number of premature failures of the building envelope. This has spurred the development of alternative construction details to manage water intrusion at the wall-window interface. Laboratory investigations focused on assessing the effectiveness of wall-window interface details to manage rainwater intrusion in the wall assembly have provided an effective way to obtain useful information on the varying performance of different interface details. Previous studies undertaken to investigate the effectiveness of details typically used in wood frame low-rise wall assemblies have shown the degree to which different details manage rainwater intrusion and the extent of fault tolerance of such systems. This paper reports on results obtained from laboratory testing of two sets of wall-window interface details and variations on their implementation, that are representative of residential and light commercial window installation practice in the United States. Results from these tests indicate that the window installations details of the type assessed in this study are adequate to manage even the most significant rainfall events as might occur in North America. It was also demonstrated that window installation designs that do not permit drainage from the sill are vulnerable to excessive water retention during significant wind-driven rain events. Additionally, critical elements for achieving functional window installation details included: Sill-pan flashing with watertight corners; openings along the interface between the sill and window flange to permit water drainage; and continuity of the air barrier system at the interface with the window frame and window. Such designs could be adopted for climate zones having heightened wind-driven rain loads such as the coastal areas of the United States subjected to severe storm events. The work is limited to evaluating the response of wall-window interface details to simulated wind-driven rain and water penetration; it does not address hygrothermal effects.